Control mechanism for hydraulic transmissions and pumps



H. THOMA CONTROL MECHANISM FOR HYDRAULIC TRANSMISSIONS AND PUMPS June 6, 1939 Filed May 4, I936 INVENTOR Tao/1 4 li /v5 ATTORNEY prevent overloading.

Patenteddune a, 1939 UNITED STATES NTBOL micnmsn For. nrnaauuo TRANSMISSIONS mm Pours Bans Thoma, Karlsruhe-Baden,

Application May 4, 1936, Serial No. 77,825

' In Germany May 9, 1935.

ZCIalma.

This invention relates to improvements in control mechanism for hydraulic transmissions and pumps and has for an object to provide improved means for regulating such devices, particularly to Another object is to provide pressure regulated means for this purpose in combination with manual setting means.

Another object is to provide such means for,

hydraulic transmissions in which either the pump member is controlled or the motor member or both.

Other objects will become apparent from the a following description taken in connection with the drawing which shows an illustrative embodiment thereof.

In said drawing:

Fig. 1 .illustrates more or less schematically a hydraulic transmission; Fig. 2, represents a modified control means therefor; and

Fig. 3 shows still another modified form invention; I s

In said drawing, P represents generally a-var iablevolume pump of any suitable construction such as the one shown in United States patent to Hans Thoma No. 1,931,969, granted October 24, 1933,'although the invention may be used with any other pump having provision for varying its volume.

M represents generally a hydraulic motor of the variable volume type'and may be of the same construction as pump P. However, for certain uses of the invention the member M may be any device utilizing fluid in its operation.

Numeral l I indicates any prime mover, such as an electromotor connected for driving the of the shaft 12 of the pump, which pump has a body 50 Thoma patent, has a body member I3, a power delivery shaft l2, and an oscillatable member H.

I Fig. 1 shows automatic control means forthe motor M but it is understood that this may be dispensed with and the volume of the motor be set fora constant amount or that even a constant volume motor be employed, such as a vane or gear motor or a cylinder and piston. Similarly,

the pump volume may be kept constant and the motor volume manually and automatically conscribed. The member I4 is shown as providedwith an extension l1 to which is pivotally attached a rod I! connected with a hand lever l9 which is pivoted to any suitable abutment 20 and is preferably provided with adjustable holding means such as a toothed segment 2| with which cooperates a latch member 22 which may be manually released by the button 23 extending from the end or the handle 24. Rod I8 is connected to lever I! by any suitable means providing for at least one way spring biased relative movement. This may. be accomplished by attaching a disk or,other spring abutment 25 to the end of rod I 3 within a cylindrical chamber 28 within which is located the spring 21. The top of the chamber may be' closed with a lid 28 which serves as an abutment or stop for the operating connections, as the rod l8 and the disk 25, said lid being provided with a suitable bracket 29 for pivotal connection with the lever l9 It will be noted that such'a mechanism provides for a manual adjustment of the member ,ll which. in the form shown, is positive-in the down-.(volume. reducing) direction but which permits of downward movement of member l4 upon the application of a force sufliciently large to compress spring 21.

In the construction shown, means is provided -for applyinga downward force (in the volume reducing direction) under control of pressure in conduit l5, or the difference in pressure in the two conduits l5 and I6. This may be accomplished by providing a cylinder 30 having a piston 3| carried by a piston rod 32 pivotally connected in the slot 44 of the extension l1. Spring 33 biases the piston 3| upwardly so that in the' absence of pressure above the piston (which space communicates with the conduit l5 through tube 34), the piston and extension l1 andmember ll are held upwardly to the maximum volume position determined by the setting of lever I9. It will be noted however, that if a predetermined pressure in conduit I5 is exceeded, as by increase of load on the motor M, the piston 3| will be forced downwardly against the action of springs of them may be omitted. If desired, the tension of the spring 33 may be made adjustable by providing a adjustable abutment therefor, as the disk 33a nd setting screw 3312.

Instead of a cylinder and piston any other expansible member, such as a metal bellows or the like, could, oi course, be employed.

It will also be seen that as soon as the load on motor M is reduced and the pressure in conduit l therefore drops, the springs 33 and 21 will cause the pump volume to be increased. If desired, a conduit 35 may be provided connecting the cylinder 30 with the conduit IS, in which event, the control means will be responsive to diil'erences in pressure in the two conduits. The conduit 35 may however be omitted and the space below the piston 3| vented to the atmosphere, in which case the control device will be actuated in accordance with gauge pressure in .conduit I5. j i

The means described therefore provide a combined manual and automatic means for controlling the output of pumps. It is immaterial how the fluid delivered by the pump is employed whether in a motor device such as shown in Fig. 1, a motor cylinder and piston for operating planers, shapers or' other tools, or whether the pump delivery is merely to a storage tank or accumulator.

If the fluid receiving member is a motor of variable volume type as shown, it may also (or in the alternative) be desirable to provide the motor with a combined manual and automatic volume varying means. One way to accomplish this is to provide a cylinder 30' containing a piston 3| and having a piston rod 32' connected in the slot 44 of the extension 11' of the oscillatablevolume varying device ll of motor M. Above said piston, a spring 33 is shown. The space below the piston is shown as connecting with the pressure conduit l5 by means of a condult34 and, if desired, the space above the piston may .be connected to the low pressure conduit l6 by meansof a conduit 35' althou h, ii desired, this space may simply be vented to the atmosphere. A spring 21 is shown as arranging to apply a force to the member M in a downward direction. The.extenslon l1 may also be provided with a pin l'l" received in a slot 43 in a rod l8 connected to the lever l9. It will be seen therefore that in the absence of pressure in conduit IS the member M will be drawn..toward its central lreduced volume) position by means of springs 21' and 33 so that its position is determined by the setting of lever 19'. Since springs 21' and 33' act together, one of them may, of course, be omitted.

Assuming the parts to be in the position shown and the motor shaft l2 delivering a certain torque and that as a result of the application of increased resistance to shaft II, the pressure in conduit I5 should rise unduly, the piston 3| will be moved upwardly and, against the action of springs 33and 21', move the member l4 upwardly, thus increasing the volume of the motor M whereby the required additional torque can be applied to the shaft l2 (at lower speed), causing the pressure in conduit l5 to be lower and thus reducing the power input.

It will be noted that in the construction described above, pressure responsive means are provided which upon the occurrence of pressurerise beyond a predetermined point cause the volume of the pump to be decreased and also increase the volume of the motor. Either of these devices may be used alone to secure the desired ellect or they may be used together.

It desired, a single means may be provided to cause the pump volume to be decreased at the same time that the motor volume is increased, and viceversa. This could be easily accomplished as shown in Fig. 2 by connecting the arm I! with the arm H by any suitable means such as a beam 45 pivoted between. its ends to an abutment '46 and suitably connected at its ends by the links 41 and 41' to the ends of arms I! and I1 respectively. In such an arrangement, of course, only one of the pressure responsive actuating devices would be needed:

With the construction shown in Fig. 1, the reaction of the pressure in cylinder 30 will affect the ease of operation of lever l9. In order to avoid this objection the construction shown in Fig. 3 may be used. Instead oi the relatively long extension ll'a shorter extension Ila may be employed to which is shown connected a link 40 pivoted intermediate its ends to a beam 4|, one end of which is connected asby link 42 to the hand lever l9 whereas the other end thereof is pivoted to the connecting rod 32. With this construction the adjustment of lever l'9 serves to adjust the fulcrum of lever 4| so that the maximum volume of the pump may be manually varied, while the volume may be automatically reduced below said maximum by the pressure responsive means described. In Fig. 3, M indicates any means for utilizing the fluid pumped by P. 'A similar arrangement can, of course, also be utilized in conmotion with the motor control means if a variable volume motor is used such as the one illustrated in Fig. 1.

'The invention is not intended to be limited to the three forms shown, which are to be understood as illustrative only and not as limiting, as

various changes in construction and arrangement may be made, all coming within the scope of the claims which follow.

I claim:

1. In 'a hydraulic transmission system including a variable volume pump, a variable volume motor and connecting conduits therebetween, volume varying controlling means for said pump and said motor, and means responsive to the pressure in said conduits for respectively inversely and simultaneously varying the volume of said pump and of said motor, said last means including a beam pivotally mounted for oscillation about a fixed axis, and links pivotally mounted near each end of the said beam and respectively pivotally interconnected with the control means on said pump and motor.

2. In a hydraulic transmission system including a variable volume pump, a variable volume motor, and connecting conduits, volume varying controlling means for said pump and said motor,

and means responsive to the pressure in one of said conduits for respectively inversely and simultaneously varying the volume of said pump and said motor, said last means including a beam pivotally mounted for oscillation about a fixed axis, and links pivotallymounted near each end of the said beam and respectively pivotally interconnected with the control means on said pump and motor.

HANS THOMA. 

